I have a 23 year old female RES. Up until 6 years ago she always lived with friends. She ended up alone because the other, smaller female she lived with became agressive and I had to seperate them. She is 8 inches long and now lives in a 90 gallon tank. I would really love to get a second female but have concerns.

I dont think my current girl would be agressive, she is very mild mannered and has never shown any agression. But I worry she is so big she could accidentaly hurt a baby, and I worry another adult could be agressive towards her. Is there a safe way to add another? Or would getting a second turtle only be selfish?

It always depend on the turtles ! Your female might be calm towards a turtle but aggressive towards another. If you want to introduce her to another turtle I would go for a bigger one than a baby. Do you have a spare tank ? Even if it's a small one, so you can separate them if things go wrong, and you'll have time to look for a proper tank for your second turtle. Keep a close eye and always be prepared to separate them whenever you think you need to.Some people are very successful with housing numerous turtles together, and some find it near impossible to do so.

I wouldn't get a "baby" since you don't know the personality. Plus, it could be another male and would grow up to harass her as well. Either way, if you have the means to separate her and the other turtle in the future, then I guess you can try. A better idea, you could look at rescues for other females to see if they get along.